1. Field of the Invention
The present invention relates to an automatic focusing device which illuminates an object by an auxiliary light source to detect a distance to the object and drives a lens to an in-focus position.
2. Description of the Prior Art
In a passive type automatic focusing device which drives a photo-taking lens to an in-focus position by utilizing a light from an object as information on the distance to the object, the device is inoperative when the object is dark. An automatic focusing device which drives the lens to the in-focus position by utilizing an auxiliary light source when the object is dark has been proposed, as shown in U.S. Pat. No. 4,327,976. However, the imaging lens driven by such an automatic focusing device is, in many cases, located at a lens position corresponding to an infinite focusing distance or a lens position corresponding to a minimum focusing distance before it is driven, and a long time is required to drive the lens to the in-focus position. When a TTL auto-focusing operation is carried out in a single lens reflex camera, an image on a finder is extremely defocused when the lens is at the position described above and it is difficult to precisely determine an in-focus position and impossible to frame the image.